A medical ventilator delivers gas to a patient's respiratory tract and is often required when the patient is unable to maintain adequate ventilation. Mechanical ventilation is the single most important therapeutic modality in the care of critically ill patients. Known ventilators typically include a pneumatic system that delivers and extracts gas pressure, flow and volume characteristics to the patient and a control system (typically consisting of knobs, dials and switches) that provides the interface to the treating clinician. Optimal support of the patient's breathing requires adjustment by the clinician of the pressure, flow, and volume of the delivered gas as the condition of the patient changes. Such adjustments, though highly desirable, are difficult to implement with known ventilators because the control system demands continuous attention and interaction from the clinician.
Ventilatory modes are methodologies for controlling the pressure, flow and volume characteristics of the breaths to be delivered, and are preset in known ventilators during the manufacturing process. Various ventilatory modes have evolved to support breathing for patients with different pathologies at different stages of the course of treatment. Examples of such modes include intermittent mandatory ventilation (IMV), assist-control ventilation (A/C), pressure support ventilation (PS) and continuous positive airway pressure (CPAP).
One limitation of known ventilators is that selection of a ventilatory mode imparts specific and often inconsistent instructions to the ventilator controls. Another problem is that modes having the same or similar names are often preset differently on different ventilators. This characteristic of known ventilators has led to unsuccessful attempts to enforce standard definitions for ventilatory modes, and has resulted in the requirement of extensive training of clinical personnel.
Another limitation of known ventilators is the difficulty and uncertainty when changing ventilatory modes. A large number of control and alarm settings are changed by the clinician to implement a new mode. While the settings are being changed, a time period of up to several minutes, the therapy delivered to the patient is uncontrolled. Typically, the clinician disconnects the patient from the ventilator and provides manual support during the transition to the new mode. In addition, clinicians are often uncertain about the breathing pattern the new mode will produce when applied to a particular patient. This discourages clinicians from trying new modes which might better accommodate the patient, and encourages prolonged use of existing modes to control the patient's breathing via the ventilator, thereby inhibiting the patient's respiratory drive. The patient spends more time than necessary on ventilatory support, leading to slower recovery and increased risk of complications.
Yet another limitation of the known ventilators is that new features, in particular new types of breaths and new ventilatory modes, can only be provided by physically changing the memory device containing the software programs. A clinician with a new type of therapy must navigate a lengthy and circuitous development path to implement the therapy on a patient. First, the clinician must explain the therapy to the representatives of a ventilator manufacturer, convince them that the therapy is commercially viable, and direct the manufacturer through several design/development cycles over a period of many months. If the therapy is shown to be beneficial, an additional lengthy delay occurs for manufacturing startup and regulatory approval. This frustrating pathway significantly inhibits the development of new types of therapy in ventilation.
A further limitation of the control interfaces of known ventilators is the provision for control of only a single mode of ventilation. The needs of patients are continuously changing, and a principal focus of ventilatory therapy is to "wean" the patient from full ventilatory support to self-supported breathing. During this transition, which can take days to weeks, the ventilator must accommodate and encourage efforts by the patient to breathe and "synchronize" its efforts with patient-induced breathing. Delivery of an optimal breathing pattern requires delivery of respiratory gas to the patient at the appropriate time and rate, and removal of the respiratory gas at the appropriate time and rate. Known ventilators require frequent encounters between the clinician and the patient to adjust the breathing pattern. Because such encounters tend to be widely spaced, patients spend long periods between such encounters "fighting" the ventilator as it tries to deliver breaths which do not match their needs.
Another limitation of the user interface on known ventilators is the separation of the control settings, the alarm settings and the patient data into different areas of focus for the clinician. The clinician is required to mentally integrate the control settings, alarm settings and patient data to determine whether the current therapy is appropriate. The ventilator interface is interposed between the clinician and the patient, obscuring both the therapy and the condition of the patient with unnecessary complexity.
For many of the reasons described above, known ventilators require a high level of skill and interaction from clinicians. Many clinicians lack the required exposure and training to command the ventilator to deliver the appropriate therapy for the wide variety of patient conditions.
It is therefore a principal object of the invention to provide a ventilator control system which is connected to a ventilator pneumatic system for controlling the selection of ventilatory modes to maintain desired pressure, flow and volume characteristics of the breaths delivered to a patient. It is another object of the invention to provide a ventilator control system that enables a clinician to prescribe a series of ventilator breaths, modes or therapies to accommodate changes in a patient's condition. It is another object of the invention to provide a ventilator control system that enables a clinician to access stored historical patient data for clinician training or patient therapy. It is another object of the invention to provide a ventilator control system that enables a clinician to create new ventilator breaths, modes or therapies on demand. It is another object of the invention to provide a ventilator control system that simulates the effect of a new ventilator mode on a patient, before actually implementing the new mode on the patient.